The present invention relates to encoders and, more specifically, encoders that are utilized with utility meters and that are able to withstand the harsh environments that utility meters are submitted to.
Utility meters, such as gas, water and electric meters, their enclosed electronics and batteries are subject to harsh environments including temperature variations that may span 180 degrees Fahrenheit, e.g., xe2x88x9222xc2x0 to 158xc2x0 F., humidity variations that can go from 5% humidity to 100% humidity, lightning strikes, rain, snow, and wind. Yet, their operation must be reliable and accurate for appropriate utility monitoring and billing.
With regard to accuracy, perhaps the most important component of a utility meter is its encoder that produces the counts that comprise the consumption reading against which utility customers are billed. As such, in the development and design of utility meters encoder accuracy is a prime factor. Current consumption by the utility meter electronics is also an important factor in the design of meters due to the limited life of the battery supplying power to the electronics.
In response to these factors, the most straightforward utility meter design approach often is to keep the circuits within the meter simple by using high-valued resistors, and a resultant high impedance encoder, to keep current consumption down. However, various types of the contamination of the meter, including contamination by moisture, compromises the operation of the high impedance circuitry and, thus, the operation of the meter. To avoid meter contamination problems, the design approach has historically been to impose constraints on the mechanical design of the meter to create a meter enclosure that will reduce the affects of the meter""s environment and to create reliable mechanical components within the meter.
However, utility meter failures of meters utilizing high impedance encoder circuits still occurxe2x80x94encoder counting errors continue to exist due to mechanical failures and/or higher than normal current flow causes a drain on the meter""s internal battery. For example, refer to the prior art configuration of a high impedance encoder that has been utilized in gas and electric meters in FIG. 1. The configuration provides for monitoring the switch at all times. When the switch is closed due to correct operation or closed due to faulty operation from contamination the impedance presented is high causing a low current and long battery life. However, faulty operation due to contamination is virtually undetectable unless other components of the utility meter fail as well. As such it has become a realization that getting high impedance encoders to reliably operate in the harsh environment to which utility meters are subject is a very demanding constraint.
Some in the art have recognized the vulnerability of a high impedance encoder within a utility meter and have addressed that vulnerability by the scaling down of the impedance of the encoder. One approach, with a focus on keeping the current consumption of the utility meter electronics controlled, has been to duty cycle the encoder sensor in combination with the scaling down in impedance the circuitry that is connected to the sensor. This approach is a reasonable one to maintain the encoder count accuracy, however, if the mechanical package of the utility meter is compromised, the current consumption of the utility meter gets very high and ultimately drains the battery resulting in meter failure.
In view of the above, there is a need for a utility meter that maintains a low current consumption via a low impedance encoder whose operation is not substantially affected by harsh environments or contamination.
The needs described above are in large part addressed by the low impedance encoder for a utility meter of the present invention. The low impedance encoder generally comprises a clock source and a switch. The clock source operates according to a predetermined duty cycle. The switch has a first position, closed, and a second position, opened. The duty cycle controls a current flow through the switch. A high current flow through the switch indicates that the switch is closed and that the consumption of a utility as registered by the utility meter has occurred; the switch will continue to open and close throughout the process of metering. A low (or no) current flow through the switch indicates that the switch is open.
The switch may be located internal to or remote from the encoder. The utility meter may be a water meter, a gas meter, or an electric meter. However, in the preferred embodiment of the invention, the utility meter is a water meter that is located remotely from the encoder and connected thereto by cabling. The use of the duty cycle within the encoder operates to substantially minimize current consumption by the encoder and thereby extend the life of the battery powering the encoder.